This invention relates generally to methods and apparatus for flow of fluids through common wall conduits and more particularly concerns methods and apparatus for juxtaposed flow of fluids separated by a folded membrane. Still more particularly, the invention is directed toward an apparatus for use in the dialysis of two fluids and relates specifically to an apparatus for the cleansing of impurities from blood by hemodialysis.
Although experimental drug and diet treatments for persons having damaged or failed kidneys have recently been suggested, the many thousands of persons suffering from chronic kidney failure still require either artificial blood purification or the drastic procedure of kidney transplant. One method of artificial blood purification, hemodialysis, involves counterflow of juxtaposed blood and a dialysate, separated by a semipermeable membrane. Hemodialysis, at present, is most commonly performed in a hospital under supervision of trained personnel. Present systems require complex, expensive equipment and facilities and, at least in part because of the great expense, are not readily available or accessible. These systems are employed for periodic treatment of the patient. Thus, during periods between treatments, blood impurities increase in concentration and the resulting ill feeling builds up until the next treatment. Further, the treatment itself is time-consuming and painful, at least in part because of the necessity of connection and disconnection of the patient's blood supply to the external apparatus.
In attempts to overcome disadvantages, complexities and expense of prior hemodialysis treatment systems, various types of simplified portable and small-size dialysis systems have been suggested.
Among these efforts have been those described in my prior U.S. Pat. Nos. 3,522,885 and 3,565,258 as well as 3,778,369. These parallel-flow hemodialyzers are designed to operate without use of an external blood pump and to employ inexpensive, readily available materials so that the unit may be discarded after each use. A major drawback of the hemodialyzers of these prior patents resides in the use of relatively expensive, in the preferred thickness, flattened cellophane tubes stacked in a case for separating blood from the juxtaposed dialysate. The assemblies employing such tubes are expensive, complex and pose some difficulties in fabrication.
Among the dialyzers employing sheet membrane rather than tubes, are those described in U.S. Pat. Nos. 3,396,849 and 3,442,388. However, these require complex and costly support arrangements for the membrane as in U.S. Pat. No. 3,396,849, or a corrugated support member to hold a membrane that is made in a corrugated form, as in U.S. Pat. No. 3,442,388. Adhesive bonding of the membrane edges to a case is a significant problem in the latter arrangement, since materials used internally of the dialyzer that may be in contact with the blood must be chosen with regard to reaction with the blood.
The present invention is an improvement on the invention disclosed in my patent application for a Folded Membrane Dialyzer, Ser. No. 233,528, which has now issued as U.S. Pat. No. 3,788,482, and is also an improvement on my patent application for Edge Sealed Folded Membrane, Ser. No. 373,160, filed June 25, 1973, which issued Feb. 4, 1975 as U.S. Pat. No. 3,864,265. The disclosures of both of these applications are incorporated herein by this reference as though fully set forth.
In U.S. Pat. No. 3,788,482, I have disclosed a dialyzer designed to be used frequently for short periods of time and which may be discarded after use. The design eliminates the need for a blood pump and also avoids the requirement of complex associated equipment and safety circuits. In particular, this apparatus is adapted for use under a program of daily dialysis at home so as to provide a more nearly continuous removal of poisons from the blood and thus avoid the increased buildup of blood contaminates that occurs with less frequent treatment.
However, the folded membrane dialyzer of this patent requires a multi-element or form-in-place case that has proven relatively expensive to fabricate. In this apparatus, end edges and side edges of the folded membrane are sealed by embedding them in a plastic material that forms a portion of the housing. Access ports for blood and dialysate are formed by removal of studs that are positioned during curing or solidification of the sealing plastic. The end edges of the folded membrane are positioned between support strips and encapsulated as a subassembly step before the stack is mounted to the remaining portions of the case. Alternatively, the case and edge encapsulation are formed in place about the folded membrane stack.
In my later application Ser. No. 373,160, improved edge sealing is achieved by use of an end fold plate, permitting encapsulation of end edges but blocking flow of liquid encapsulating material into the flow ports. The arrangement of the prior application Ser. No. 373,160 is effective and efficient, and has proven to be satisfactory. Yet, because of the nature of the use of the apparatus for hemodialysis, and particularly because of its use as a disposable instrument, it is of critical significance to achieve improved ease and cost of fabrication and increased reliability. In the prior application Ser. No. 373,160, sealing of the end edge, like the sealing of the serpentine side edge, is achieved by a solidified liquid encapsulating material. The arrangement requires flow of such material over relatively long distances, between the several injection channels that are spaced along the length of the apparatus. This requires relatively high pressure of the injected liquid encapsulating material which may act to compress the membrane stack during the injection. If the encapsulating material solidifies before the compression of the stack is relieved to allow the stack to return to its desired configuration, the flow channels may be degraded. On the other hand, if the stack is allowed to return to a substantially uncompressed condition, the still-liquid encapsulating material is forced back out through the injection channels and must be removed from the exterior surface of the apparatus. Furthermore, in some cases it may be desirable in the apparatus described in my copending application Ser. No. 373,160 to achieve liquid encapsulation of the side edges as a first step, and allow curing time before accomplishing encapsulation of the end edges or vice versa. In either case, additional time for the two-step curing is undesirable from the standpoint of economy of manufacture.
Accordingly, it is an object of the present invention to provide improved edge sealing for the folded membrane of a fluid flow transfer apparatus.